Chapter 13-16 Flashcards
Mendel
The father of modern genetics, disapproved the blending theory with his work with garden pea plants. Provided the basis for what we know about inheritance today
Dominance (Complete Dominance)
If you have to different alleles the one that is apparent is the dominant allele, represented by a capital letter
Recessive Allele
If you have two different alleles the one that is hidden, is called the recessive allele and is represented by a lower case letter
Homozygous
If an individual has both the same alleles (AA or aa)
Heterozygous
If an individual has different alleles (Aa)
Theory of Segregation
An individual inherits a unit of information (allele) about a trait from each parent. An individual passes on only one of their alleles to his offspring, and the other allele comes from the other parent. During gamete formation, the alleles segregate from each other
Tracking Generation
Paternal generation mates to produce (P), first generation offspring mate to produce (F1), second generation offspring (F2)
Mendels Monohybrid Cross Results
F2 plants showed dominant to recessive ratio that averaged 3:1
Genotype
Combination of alleles that an individual has (Aa, aa, AA)
Phenotype
The expressed trait that an individual has (Brown eyes, green eyes, blue eyes)
Gene
A unit of DNA that codes for a specific trait, passed down from parent to offspring
Allele
A different form of a gene, example gene codes for eye colour (blue, green, brown)
Multiplication Rule
If the occurrence of one event does not affect the probability of another event then the probability of their joint occurrence is the product of their independent probabilities. (Often when gender is specified)
Test cross
If an individual has the recessive trait, we know what his genotype is aa, if an individual has the dominant trait we cannot be certain what his genotype is, AA or Aa. To perform a test cross you mate the individual in question with an individual who is homozygous recessive, an examination of the offspring will tell you the genotype of the individual in question
Incomplete Dominance
Occurs when neither of the two alleles are dominant over the other, the traits blend together. A heterozygote would have a trait that is intermediate between the paternal traits. Example red and white parent flowers produce pink flowers.
Co-dominance
Occurs when both of the alleles are expressed, both are dominant. Example: RR and WW, F2 generation displays a 1:2:1 ratio
Multiple Alleles
Occurs when more than 2 alleles determine the individuals phenotype. No set number of alleles that can control a trait, called allelic series
Example: ABO blood typing in humans
ABO Bloodtyping
The A allele (I^A) and B allele (I^B) are codominant and both are dominant to the O allele (i)
Monohybrid Crosses
Considers the inheritance of one trait
Dihybrid Crosses
Considers the inheritance of two traits
Independent Assortment
Genes for 2 traits can go together in different combinations, due to the different ways that the chromosomes can line up during meiosis 1 when gametes are being made.
Example: GgYy could pass on GY, Gy, gY, gy
Polygenic Inheritance
Continuos traits are controlled by
More than just one gene. A group of genes that all contribute to the same trait are called polygene
Continuous Traits
Some traits do not appear as one form or another but as a whole range of possibilities
Example: Human Height
Independent assortment of genes on the same chromosome
Genes that are located on the same chromosome do not assort independently, the genes will be passed on together because it is the chromosomes that are distributed in the gametes.
Linked Genes
Genes on the same chromosome
Chromosomal Theory of Inheritance
States that genes are located on chromosomes and chromosomes are passed on to offspring. If 2 genes are located on the same chromosome then they will be passed on together to the offspring
Sex linked traits
Genes located on a sex chromosome
Examples of sex linked traits
Hemophilia, red-green color blindness, duchenne’s muscular disorder
Discovery of sex linkage and result
Discovered a white eyed male when the wild type eye color is red. Concluded that the gene for eye color is located on the X chromosome, there is no corresponding eye color site on the Y chromosome. Since the mutant allele is recessive a female must receive two copies of this gene for this trait while males only have to receive one copy for this trait.
Characteristics of Sex Linkage
More males than females show the recessive phenotype, no father to son transmission but all daughters are carriers, one half of sons from carrier mothers will be affected
Colour Blindness
Red-green color blindness is X linked
Barr Bodies
The non-functioning X chromosome in a female, each cell in a females body only has 1 functioning X chromosome. Which chromosome is inactivated is random in every cell
Crossing over Mechanism
Crossing over occurs during prophase 1, and it occurs between homologous chromosomes at Chiasmata. The farther apart two linked genes are the greater probability for crossing over.
Gene Mapping
The percentage of crossing over can be used to map the distance between linked genes on a chromosome, each crossing over percentage=one map unit
Crossing over Frequency
Proportional to the distance that separates genes
Calculating Map Distance (map units or crossing over frequency)
Map distance= number of recombinant types/ total number x100
Pedigree Analysis
First thing you must do is determine the mode of inheritance, sex linked or autosomal. If autosomal is it dominant or recessive, then fill in the genotype a of the individuals
Sex linked pedigree analysis
There is significantly more affected males than females, if there is close to the same number of males and females it is autosomal. Mode of transmission is generally from the mothers side to her sons.
Dominant vs recessive
For dominant traits you need only one of the traits alleles to express that trait (AA or Aa). For recessive traits you need both of the traits alleles to express that trait (bb)
Recessive pedigree analysis
If the traits skips a generation it is likely a recessive trait
Example: two people without the trait have a child with the trait, this could not happen if the trait was dominant
Dominant
An easy way to tell if a trait is dominant is that at least one affected individual will be doing in every generation. In a pedigree if every affected individual has at least 1 parent who is also affected you can assume the condition is dominant.
Example: two people with the trait have a child who does not have the trait- means it is dominant
